There are a substantial and varied number of industrial and non-industrial uses for precision vibratory instruments. For instance, vibrating belts and platforms are used in packaging and manufacturing plants for assisting in the separation of mass produced goods or parts. Further, there are many types of vibratory tools which require drivers which can provide very precise frequency and voltage/current for controlling vibration. One such tool for which the present invention is particularly adapted is a dental air-abrasive tool. The tool basically comprises a system for delivering an abrasive laden stream of pressurized air through a nozzle. The abrasive laden air stream is used to cut, excavate or etch teeth. At lower delivery pressures, it also can be used for cleaning teeth. Different delivery pressures and/or abrasive particle delivery rates are used for different applications. Thus, it can be seen that the delivery rate of abrasive particles, i.e., particles per unit volume or particles per unit time must be precisely controlled for the tool to operate well in a given application.
In operation, abrasive particles are fed from a chamber into a pressurized air stream. The abrasive laden air stream is delivered to the teeth through a hand-held nozzle assembly. FIG. 1 illustrates an exemplary system for delivering the abrasive into the air stream. The system includes a sealed lower chamber 175 mounted on a base 176 and an abrasive powder supply vessel 177 which is bolted or otherwise fastened to the top of chamber 175. Located within chamber 175 is an upwardly open cylindrical particle feed receptacle 178 which is mounted on a vibratory device 179, as particularly described in U.S. Pat. No. 4,708,534, which is incorporated herein by reference. Cylindrical feed receptacle 178 is provided on its inner surface with a helical feed groove 180, the lower end of which communicates with the bottom of the cylinder and the top of which is in communication with a feed tube 181 which delivers the particulate material through a section of resilient, flexible tubing 182 to an exit tube 183 which passes through the wall of vessel 175. Joined to tube 183 is a second section of resilient flexible tubing 184 which is in turn connected to a duct 172 through which pressurized air is flowing to the nozzle 108 of a handpiece 107.
Powder supply receptacle 177 is adapted to receive and contain a supply of abrasive particulate matter, generally indicated by the reference character P and to supply the same in a uniform manner to the bottom of cylindrical feed device 178 through a feed tube 186 in a manner more particularly described in the aforementioned U.S. Pat. No. 4,708,534.
In order to bring the powder delivery system up to a pressure at which it is primed for operation, air under pressure, for example, about 80 psi, is delivered to chamber 175 by way of a connection 187 which is connected to line 160 which is pressurized upon closure of a valve (not shown). A branch conduit 188 also supplies air at the same pressure to the powder supply chamber 177 by means of a connection 187 which communicates with the interior of the supply chamber.
Vibratory device 179 is an electrically operated device which is preferably activated off handpiece 107. In general, the rate of vibratory feed is controlled by way of an adjustable control device 190 mounted on the equipment control panel in a convenient location. Device 190 may be set manually by the operator to a desired vibratory rate or optionally may be a pressure responsive device which automatically adjusts through connections to switch 191 so that an appropriate rate is provided for the operating pressure level as selected on switch 191.
The abrasive delivery system is also preferably provided with a normally closed pinch valve 192. Pinch valve 192 is controlled by a solenoid 193 either directly or through a fluid pressure device. The solenoid 193 is preferably energized upon closure of a switch activated off the handpiece to maintain pinch valve 192 in the open position whenever vibrator 179 is in operation.
In summary, when activated, chambers 175 and 177 are immediately pressurized at the low end of the operating pressure range so that the abrasive delivery system is readied for the delivery of a particulate-laden air stream through resilient tube 184 to conduit 172 when desired by the operator. Upon activation of the vibrator and opening of pinch valve 192 by the control circuitry, described hereinafter, particulate material advances upwardly within spiral groove 180 through duct 181 where it enters resilient, flexible tubing 182 and exit tube 183, where it exits container 175 and passes through tube 184 to join conduit 172.
It should be apparent that the amount of abrasive delivered into the air stream is primarily a function of the frequency and amplitude of vibration of the spiral groove 180.
Typically, the vibratory means 179 is an electromagnetic coil system similar to what might be found in an audio speaker. In particular, an oscillating current is provided to a magnetic coil. An armature is placed proximate (e.g., within) the coil. The magnetic field created by the current running through the coil exerts a force on the magnetic armature causing it to move. An AC current in the coil will cause the armature to move back and forth at the AC frequency of the current. The armature is coupled to the vibratory device 179 which, in turn, is mechanically coupled to the helical feed 180, causing it to vibrate.
FIG. 2 illustrates an exemplary drive circuit of the prior art for driving the vibratory device 179. In this typical system, the coil drive circuit consists of a switch 200, rectifier diode 202, a rheostat 204. The driving circuit is powered directly off the AC line power. The switch 200 activates the delivery system. The rectifier diode 202 half-wave rectifies the alternating current. The rheostat 204 steps down the voltage relative to the input voltage to the desired level.
The vibratory feeder drive of the prior art as exemplified by FIG. 2 has significant disadvantages. For instance, the signal to the vibratory device 179 is directly line driven. Accordingly, the voltage and the frequency of the drive signal is not particularly stable. Specifically, as is well known, line power can fluctuate significantly in both voltage and frequency in most parts of the world.
Further, depending on the locality, the line AC frequency can differ. For instance, in the United States, standard AC line power is provided at 60 hertz. However, in Europe, standard AC line power is provided at 50 hertz.
Typically, the chamber 177 is designed and dimensioned to have a resonance frequency at or near the frequency of vibration, i.e., 50 or 60 hertz depending on the power supply of the country for which the device was designed. This provides for stable and large magnitude vibration with small power requirements. Accordingly, a tool optimized to operate at 60 hertz line power will not operate as effectively on 50 hertz power and vice versa since the vibrations will not be as close to the resonance frequency of the vibratory system as it could be.
In the drive systems of the prior art as exemplified by FIG. 2, the vibration frequency is dictated by the local power supply and cannot be altered. Thus, it is difficult to use a single tool in different localities with different line power frequencies.
Accordingly, it is an object of the present invention to provide an improved dental air-abrasive delivery tool.
It is a further object of the present invention to provide an improved drive circuit for driving a vibrator for supplying abrasive into an air stream in a dental air-abrasive tool.
It is another object of the present invention to provide an improved drive circuit for any vibratory apparatus.
It is yet another object of the present invention to provide a drive circuit for a vibratory apparatus which can provide a drive signal of essentially any frequency or voltage regardless of the local power supply.
It is yet a further object of the present invention to provide a drive circuit for a vibratory apparatus which is extremely stable in both voltage/current and frequency.